sysvinit, upstart: handle symlinks to dirs in /var/lib/ceph/*

Match a symlink to a dir, not just dirs.  This fixes the osd case of e.g.,
creating an osd in /data/osd$id in which ceph-disk makes a symlink from
/var/lib/ceph/osd/ceph-$id.

Fix proposed by Matt Thompson <matt.thompson@mandiant.com>; extended to
include the upstart users too.

Fixes: #5490
Signed-off-by: Sage Weil <sage@inktank.com>
Reviewed-by: Dan Mick <dan.mick@inktank.com>